Search

Neutrons generated by the deuterium-tritium reaction (D-2 + T-3 --> n + alpha) are correlated to the alpha particle by energy and momentum conservation to lie along trajectories 180degrees with respect to one another. An associated particle neutron generator uses this spatial correlation to infer the neutron trajectory by detecting the alpha particle. This technique can be used to suppress backgrounds and in building three-dimensional images using the return excitation gamma-ray energy due to the neutron interactions. The critical-performance component of the system is the alpha detection element, which is embedded within the neutron generator accelerator head. This element must be highly efficient, capable of nanosecond timing, and robust under the temperature changes encountered during manufacture. ZnO(Ga) scintillator coatings of differing thicknesses, with and without Ni overcoatings, were evaluated for this purpose, when excited by alpha particles between 3.2 and 5.4MeV. Average light output of up to 61 photoelectrons per event was measured. (C) 2003 Elsevier Science B.V. All rights reserved.

We have performed a search for Sarin, a chemical warfare agent, in luggage-sized sealed containers in order to illustrate how effectively and quickly a search could be conducted in a fixed installation at airports, embassies, government buildings, military installations, and other public areas. A portable neutron generator and a Californium source were used, generating up to 10(8) neutrons per second, that penetrate into a container and are capable of exciting a sample in a period of approximately 10 s, to produce enough gamma radiation that target elements within the sample can be identified. In the vast majority of cases, there is no chemical agent present, so the question becomes how long to search. We show results of tests for sensitivity of this technique as a function of time. We have also developed background or typical samples with no chemical agent present to estimate the false positive rate for this technique. (C) 2003 Published by Elsevier Science B.V.